It is possible for the feed system to have a low impedance, looking downstream from the pressure source at a certain frequency.

在压力源下游，供应系统在某一频率下可能有一低的阻抗。

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So far there has been no pressure from the stock market (the only pressure source Congress seems to respond to), and so no effort to act as the March 1 sequester deadline approached.

FORBES: Markets Can Handle Anything, Even A Sequester

In recent weeks, the floors in that part of the mine had been "heaving, " or buckling up, from intense pressure, said the source, who has intimate knowledge of the conditions in the mine.

CNN: Camera lowered into mine cavity shows 'survivable space'

If you're looking for more technical details you'll find a link to the recently published paper titled, Dexterous manipulation of microparticles using Bessel-function acoustic pressure fields at the source.

ENGADGET